Rope is often used to displace an object. The object is supported by a distal portion of the rope, and a proximal portion of the rope is displaced to place the rope under tension and thereby displace the load. To displace the proximal portion of the rope, a winch device is often used. Examples of winch devices include a drum or spool winch, a windlass, and a capstan. The winch device may be human powered or motorized. In either case, the winch provides a mechanical advantage. When human powered, although human effort is required, the winch eliminates the need to grip the rope. When motorized, the winch eliminates the need for human effort altogether.
A winch typically defines an engaging surface that can take many forms. For a winch employing a drum or spool, the engaging surface is essentially cylindrical, often having side walls. For a winch in the form of a capstan or windlass, the engaging surface can be cylindrical or can define an annular cavity the cross-sectional area of which decreases towards the axis of rotation.
With any form of winch, at least an active portion of the rope is wound around the drum such that, when the drum is rotated about a longitudinal drum axis, friction causes a working portion of the rope under tension to be displaced along a pulling axis. For many winch systems, a stored portion of the rope can be stored on the drum; for other winch systems, such as when the winch takes the form of a capstan or windlass, the stored portion of the rope is stored separate from the winch. The friction may be between the active portion of the rope and the engaging surface or between the active portion of the rope and a stored portion of the rope already wound around the drum.
Loads on the active portion of a rope that is being displaced using a winch thus include tension loads that extend between the winch and the load, bearing loads directed radially inwardly towards the axis of the winch, and compression loads directed inwardly towards the longitudinal axis of any portion of the rope.
In the case of a winch having a drum or spool, the active portion of the rope engages the stored portion of the rope wrapped around the drum or spool. The stored portion of the rope defines shallow grooves between adjacent stored portions. The bearing loads on the active portion of the rope tend to pull the active portion of the rope down into these grooves. Compression loads on the active portion of the rope tend to deform the active portion of the rope to fit into the grooves formed by the stored portion of the rope. As the spool turns, the active portion of the rope is wound onto the drum and becomes the stored portion. The stored portion is no longer under significant tension load, but still may lie within a groove.
In another case, the rope may be taken up by a capstan or windlass having a friction surface defined by an annular V-shaped groove. The active portion of the rope is fed into the V-shaped groove. The slanted sides defining the V-shaped groove increase friction between the capstan or windlass and the rope but apply compression loads on the active portion of the rope. These compression loads tend to deform the rope such that the rope is forced towards the bottom of the V-shaped groove.
Accordingly, one or both of the active portion and the stored portion of the rope may be forced into a groove and become bound within the winch. When a rope is bound within the winch, the displacement of rope by the winch or the removal of the stored portion of the rope from the winch may be disrupted.
The need thus exists for rope structures and rope displacement systems and methods for lifting, lowering, and/or pulling ropes that are less susceptible to binding when displacing rope using a winch or unwinding rope from a winch.